1. Field of the Application
The invention relates to showerheads for plasma processing chambers, such as for Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), and etching of films.
2. Related Art
Apparatus of plasma processing, such as, e.g., plasma enhanced chemical vapor deposition of films, utilize showerhead to introduce the gases into the chamber. Various showerheads for plasma chambers are known in the art. The showerhead delivers processing gas into the plasma processing chamber. Some of the issues considered in designing a showerhead include proper mixing of the gas, control over the distribution of the gas throughout the chamber, control over the temperature of the showerhead and gases within the showerhead, pitting of the showerhead by plasma species, rate of gas delivery, complexity and cost of production, and more.
The design of the showerhead assembly is critical, as it directly affects the quality of the process in the plasma chamber. For example, the design of the showerhead directly affects the uniformity of the film deposited in PECVD chambers. Uniformity of deposited film becomes more difficult to control as the size of the substrate increases, for example when processing large substrates for LCD or thin-film solar panels. Uniformity is also more difficult to control when performing batch processing, i.e., when forming film on several substrates concurrently in the same chamber. However, as is evident these days, the sizes for LCD becomes larger and larger, and recent popularity of solar panels increases the demands on systems for forming high quality films on large substrates or on multiple substrates concurrently.
One problem with the current state of the art showerhead is its complexity and cost of manufacturing, mainly due to the side and shape of the gas diffusion holes. FIG. 9 illustrates a partial view of a showerhead according to the state of the art, in a cross-section view. As seen in FIG. 9, there are many gas diffusion holes having a complex and expensive shape to manufacture. First holes 900 of small diameter d are drilled from the top surface, generally using a small diameter dill bit that has very limited length, and must be replaced multiple times during the manufacture of a single part. Then holes 905 of larger diameter are drilled from the bottom surface. In this step it is very important that the bottom holes 905 be coaxially aligned to the top holes 900, which complicates the fabrication of the showerhead. Also, chamfers 910 and 915 need to be fabricated, which further increases the cost of fabrication. Moreover, due to the small diameter d of holes 900, conventional sand blasting treatment of the showerhead cannot be performed, since it clogs the holes. Therefore, special chemical cleaning must be done instead, followed by close inspection under magnification of all holes to ensure they are all open.